It has been pointed out in [1]}, [2]} that given the formula (REF ), the entanglement entropy of a subregion \(R\)  in the boundary CFT can then be represented as the volume of a corresponding region \({\diamondsuit _R}\)  (called causal diamond) in the kinematic space:
\(S(R) = {V_{kin}}{\rm {(}}{\diamondsuit _R}).\) 
